The present invention relates to a fuel injector.
German Patent No. 195 34 445 describes a fuel injector having a valve body in which a valve needle is coaxially guided. The valve body has a connection piece through which fuel is supplied to the fuel injector. The valve needle is provided with a central borehole. On the outside the valve needle is sealed with respect to the surrounding valve body. In order to actuate the valve needle, the latter is provided on the inlet side with a pressure shoulder, which works together with a piezoelectric actuator. The pressure shoulder is permanently connected to the valve needle and is guided tight on the valve body on the inlet side. This protects the actuator against the effect of the fuel pressure.
A disadvantage of this known fuel injector is that the pressure shoulder is movably guided in the valve body in order to allow the fuel to be injected, forming at the same time a sealing surface with the valve body to protect the actuator against the very high fuel pressure. The valve needle is sealingly and movably guided in the valve body also on the injection side, resulting in a number of disadvantages.
Because the valve needle is permanently connected to the pressure shoulder, the valve needle on the injection side and the pressure shoulder on the inlet side are sealingly and movably guided in the valve body, manufacturing is relatively complicated and the valve needle of the fuel injector is subject to bending and stresses and the relative positions of the two sliding surfaces subject are to being modified.
Because the pressure shoulder, i.e., the valve needle is movably guided with respect to the valve body, the sealing surface is wetted with fuel and, due to the high fuel pressure, the fuel may flow toward the actuator. Thus, the actuator is only protected against the effect of the fuel pressure but not against the effect of the fuel.
Due to the seal between the pressure shoulder, i.e., the valve needle and valve body, friction losses occur when the fuel injector is actuated. This negatively affects the shapability of the fuel injection, the switching times of the injector are increased, the actuator power is less efficiently utilized and fuel injector wear is increased. In particular, the seal at the sealing surfaces between the pressure shoulder, i.e., the valve needle and the valve body deteriorates during operation.
The fuel injector according to the present invention has an advantage of a simple, more cost-effective, low-wear, friction-free and considerably more compact design. Furthermore, according to the present invention, the seal is independent of the design of the valve needle and can therefore be integrated into a plurality of fuel injectors.
The gasket sheet is a circular gasket sheet and therefore can be particularly easily inserted into a fuel injector without a central hole having a round radial cross-section.
The gasket sheet has at least one recessed, radial flow-through segment formed by a cutout, to conduct the fuel. Thus part of the fuel line is integrated in the gasket sheet, whereby fewer components are needed, resulting in a more compact design of the fuel injector.
The gasket sheet has a baseplate and a spacer, the baseplate having a cylindrical design and the spacer having at least one radial cutout, or recess the fuel channel being formed by the cutout. The baseplate, which is inexpensive due to its simple design, can therefore be installed in the fuel injector independently of the other components of the gasket sheet. Another advantage is that, due to the separate installation of the spacer, the radial direction of the fuel channels can be selected independently of the other components of the gasket sheet, which simplifies the adjustment of the direction of the fuel channels in particular.
The gasket sheet has at least one borehole through which at least one electrical lead is run to the actuator, the borehole being sealed with respect to the fuel. Thus, the seal of the electrical lead with respect to the fuel is integrated into the gasket sheet, making an additional seal unnecessary and thus resulting in a more compact design.
The borehole is sealed with respect to the fuel by a peripheral weld, resulting in a simple, load-bearing and low-cost seal of the electrical lead with respect to the fuel.
The seal has a pot-shaped, elastically deformable actuator housing which is connected to the gasket sheet so that the actuator is hermetically enclosed by the actuator housing and the gasket sheet. This allows the actuator to be installed in the seal in a particularly easy manner, even possibly prior to being installed in the fuel injector, which can make it easier to test the seal for tightness.
The gasket sheet is connected to the actuator housing by a permanent joint, for example by a weld, providing a load-bearing, low-cost and no-wear seal, which retains its integrity for the duration of operation.
The pot-shaped, elastically deformable actuator housing has an elastically elongatable area, having an undulated design in the axial direction, which radially encloses the actuator, allowing a large actuator stroke in the actuator housing.
The pot-shaped elastically deformable actuator housing forms a pressure-tight chamber with the gasket sheet, relieving the fuel pressure on the actuator.
The actuator acts upon the valve needle via the pot-shaped, elastically deformable actuator housing, sealing the actuator with respect to leakage fuel that may occur in the area of the moving valve needle.